1. Field of the Invention
This invention relates to an internal combustion engine and, more particularly, to a valve drive mechanism for an internal combustion engine.
2. Description of the Related Art
Japanese patent publication JP-A-2001-73729 describes a valve drive mechanism for an internal combustion engine. In this patent publication, the internal combustion engine comprises an engine outer shell or body that is formed by a crankcase and a cylinder that protrudes from the crankcase. The valve drive mechanism includes a drive gear mounted to a crankshaft that is, in turn, supported by the crankcase. A rotating shaft is supported on the engine outer body by a bearing. A driven gear is mounted to the rotating shaft and meshes with the drive gear. A drive pulley is mounted to the rotating shaft. A driven pulley, in turn, is mounted to a camshaft that is supported by the cylinder. A transmitter member (e.g., a belt) is stretched over the drive pulley and driven pulley. In this device, the drive and driven gears form a reduction gear between the crankshaft and the camshaft to reduce the size of the overall valve drive mechanism.
In the valve drive mechanism described above, when the internal combustion engine is operated, part of the drive force outputted from the crankshaft is transmitted to the camshaft through the drive gear, the driven gear, the rotating shaft, the drive pulley, the transmitter member and the driven pulley in this order. Then, the intake and exhaust valves are moved in association with the camshaft to maintain operation of the internal combustion engine.